1. Field of the Invention
This invention relates generally to motion detector systems and more particularly, to electromechanical motion detectors particularly used for sensing light-weight objects.
2. Description of the Prior Art
A number of different technologies are used for motion detection. Mechanical motion detectors such as a turnstile are well known. Other smaller mechanical detectors can be used for motion detection but such detectors often lack sensitivity for light-weight objects. Other motion detectors are electromechanical in nature, e.g. pressure gauges.
Optical motion detectors normally exhibit greater sensitivity than mechanical detectors but, like mechanical detectors, each motion detector unit requires a separate assembly when incorporated into a system.
One motion detector which exhibits greater sensitivity utilizes a laminar piezoelectric film (such as KYNAR) which has printed silver on both sides of the layer of film. The laminar film is mounted on a substrate, for example polyester. When an object strikes the unit the physical vibrations caused by the contact generate a potential across the printed silver electrodes and thus the motion of the object under consideration can be electrically detected by the voltage pulse. Another problem with the piezoelectric film is its expense and the fact that a lamination process is necessary to attach the piezoelectric film to the substrate thereby causing additional manufacturing and design difficulties.
Another motion detector is a conventional electronic keyboard, such as a MYLAR keyboard wherein a key is disposed above an electrical contact. In this case the object whose motion is to be detected is a human finger and so the motion not only requires control but is indeed intentional. Thus this type of system is impractical for detectors intended to detect random motion.